1. Technical Field
An aspect of the present invention relates to a screen printing machine for forming a print of paste such as cream solder on a board. Another aspect of the present invention relates to an electronic component mounting system including the screen printing machine. Yet another aspect of the invention relates to a screen printing method.
2. Description of Related Art
Screen printing is known as a method for forming a print of paste such as cream solder or conductive paste on a board in an electronic component mounting process. In this method, a paste print is formed on a board through pattern holes that are formed so as to conform to print subject portions. A paste print is formed on a board that is set on the bottom surface of a mask plate by filling the pattern holes with paste by a squeegeeing operation of moving a spatula-shaped squeegee member in a horizontal direction with its bottom end pressed against the mask plate.
In recent years, with the demand of productivity increase and increased difficulty of printing due to reduction of the pitches of printing portions on boards, it has become an important issue to supply sufficient amounts of paste to printing portions even in the case of a high-speed squeegeeing operation. One means for satisfying this requirement is a method that uses two kinds of squeegee members, that is, a filling squeegee and a scraping squeegee (refer to JP-A-H11-042763, for example). In the method disclosed in JP-A-H11-042763, two scraping squeegees are provided, which are elevated or lowered being driven via drive shafts of a vertical driving device. Further, a filling squeegee which is also elevated or lowered being driven via a drive shaft of the vertical driving device is provided between the two scraping squeegees. The filling surface of the filling squeegee is formed so as to be inclined with respect to a mask plate by a prescribed angle.
In a squeegeeing operation of the screen printing machine disclosed in JP-A-H11-042763, the filling squeegee is moved over the mask plate in a state that a prescribed clearance is set between the bottom end of the filling squeegee and the mask plate. This makes it possible to supply sufficient amounts of paste to printing portions on a board by increasing the filling pressure at the time of filling the pattern holes with paste by means of the filling surface of the filling squeegee. Paste remaining on the mask plate after passage of the filling squeegee is scraped off by the scraping squeegees.